user manual

Functional Description

4-18

Local Bus Time-out

The MVME177 provides a time-out function for the local bus. When

the timer is enabled and a local bus access times out, a Transfer

Error Acknowledge (TEA) signal is sent to the local bus master. The

time-out value is selectable by software for:

❏ 8 µsec

❏ 64 µsec

❏ 256 µsec

❏ Infinite

The local bus timer does not operate during VMEbus bound cycles.

VMEbus bound cycles are timed by the VMEbus access timer and

the VMEbus global timer. Refer to the VMEchip2 in the Single Board

Computers Programmer's Reference Guide for detailed programming

information.

Module Identiﬁcation

Software distinguishes between an MVME177 module and an

MVME176 module by use of the I/O control register (GPI) bit 3. On

an MVME177, the I/O control register (GPI) bit 3 is out (open) for a

ÒhighÓ (one). On an MVME176, the I/O control register (GPI) bit 3

is hardwired in (shorted) for a ÒlowÓ (zero).

Timing Performance

This section provides the performance information for the

MVME177. Various MVME177s are designed to operate at 50 MHz

or 60 MHz (when supported by 060).

Local Bus to DRAM Cycle Times

The PCCchip2 and VMEchip2 have the same local bus interface

timing as the MC68060, therefore the following cycle times also

apply to the PCCchip2 and the VMEchip2. Read accesses to